كتاب الفتن
Afflictions and the End of the World
Chapter: “And fear the Fitnah which affects not in particular those among you who do wrong….”
Sahih al-Bukhari 7048

Narrated Asma':

The Prophet (ﷺ) said, "I will be at my Lake-Fount (Kauthar) waiting for whoever will come to me. Then some people will be taken away from me whereupon I will say, 'My followers!' It will be said, 'You do not know they turned Apostates as renegades (deserted their religion).'" (Ibn Abi Mulaika said, "Allah, we seek refuge with You from turning on our heels from the (Islamic) religion and from being put to trial").

حَدَّثَنَا عَلِيُّ بْنُ عَبْدِ اللَّهِ، حَدَّثَنَا بِشْرُ بْنُ السَّرِيِّ، حَدَّثَنَا نَافِعُ بْنُ عُمَرَ، عَنِ ابْنِ أَبِي مُلَيْكَةَ، قَالَ قَالَتْ أَسْمَاءُ عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ ‏ "‏ أَنَا عَلَى، حَوْضِي أَنْتَظِرُ مَنْ يَرِدُ عَلَىَّ، فَيُؤْخَذُ بِنَاسٍ مِنْ دُونِي فَأَقُولُ أُمَّتِي‏.‏ فَيَقُولُ لاَ تَدْرِي، مَشَوْا عَلَى الْقَهْقَرَى ‏"‏‏.‏ قَالَ ابْنُ أَبِي مُلَيْكَةَ اللَّهُمَّ إِنَّا نَعُوذُ بِكَ أَنْ نَرْجِعَ عَلَى أَعْقَابِنَا أَوْ نُفْتَنَ‏.‏
Reference : Sahih al-Bukhari 7048
In-book reference : Book 92, Hadith 1
USC-MSA web (English) reference : Vol. 9, Book 88, Hadith 172
  (deprecated numbering scheme)